1. Field of the Invention
This invention relates to an improvement of pneumatic tires usually used for the smooth running of automotive vehicles inclusive of truck and bus particularly driven under high loading. More particularly, it relates to a tread pattern in the pneumatic tire having improved wet performance for ensuring safe movement under rainy state.
2. Description of the Prior Art
Generally speaking, there have hitherto been known the following countermeasures for the improvement of wet performance, but they have still problems as mentioned below.
1. A rubber having a rich content of SBR is used as a tread rubber. This brings about the degradation of heat build-up performance and has a restriction in the application to high-speed running or heavy load tires.
2. The drainage ability is enhanced by the enlargement of groove width or the increase of the number of grooves. This is accompanied with the reduction of rigidity in ribs and cannot avoid the degradation of wear performance.
3. Sipes are arranged in the rib. This produces a cutting action to water stream based on an edge effect in the ground contact area of the tread, but is difficult to simultaneously establish the cornering property and braking or traction property.